Phosphorylation of the Neurospora clock protein FREQUENCY determines its degradation rate and strongly influences the period length of the circadian clock
2000
Liu, Y. | Loros, J. | Dunlap, J.C.
Under free running conditions, FREQUENCY (FLQ) protein, a central component of the Neurospora circadian clock, is progressively phosphorylated, becoming highly phosphorylated before its degradation late in the circadian day. To understand the biological function of FLQ phosphorylation, kinase inhibitors were used to block FLQ phosphorylation in vivo and the effects on FLQ and the clock observed. 6-dimethylaminopurine (a general kinase inhibitor) is able to block FLQ phosphorylation in vivo, reducing the rate of phosphorylation and the degradation of FLQ and lengthening the period of the clock in a dose-dependent manner. To confirm the role of FLQ phosphorylation in this clock effect, phosphorylation sites in FLQ were identified by systematic mutagenesis of the FLQ ORF. The mutation of one phosphorylation site at Ser-513 leads to a dramatic reduction of the rate of FLQ degradation and a very long period (>30 hr) of the clock. Taken together, these data strongly suggest that FLQ phosphorylation triggers its degradation, and the degradation rate of FLQ is a major determining factor for the period length of the Neurospora circadian clock.
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